There have been many different types of separators and methods for removing or cleaning undesirable debris from a desired granular material. For example, reference may be made to the following U.S. Pat. Nos. 456,448; 2,967,616; 3,341,012; 3,468,418; and 4,226,709.
While such prior known devices may have been successful for some applications, it has been difficult, if not impossible, to separate or remove undesirable debris, such as fines and overs from grain, in a highly efficient and effective manner, without using very expensive and extremely complex equipment. In this regard, for example, in U.S. Pat. No. 2,967,616, there is shown a separator having a vibrating scalping screen for permitting large foreign material in the grain (sticks, stones, etc.) to be removed. The grain drops through the scalping screen onto a second vibrating screen which removes large foreign grain (corn from wheat, etc.) As the grain passes over the second vibratory screen, it drops onto a third vibrating screen where the fines are removed through this screen. The clean graded and separated grain is then carried over the third screen into a discharge chute for collection.
While such a system may be satisfactory for cleaning granular material for some applications, it has proven to be less than totally satisfactory, in that it has caused other problems. In this regard, the resulting flow of granular material over the screens due to their vibrating motion can cause the material to sheet if the screens are vibrated too slowly. Alternatively, if the screens are vibrated too rapidly, the granular material runs with the debris. The desired granular material, such as grain, is carried with the unwanted debris and is discharged and lost with the unwanted material, such as overs and fines.
Therefore, it would be highly desirable to have a new and improved method and apparatus of separating heavier debris from the lighter granular material in a more efficient and cost effective manner. Such a method and apparatus should reduce greatly the loss of the desired granular material with the debris.
Separators, and more particularly vibrating screen type separators, have been used in the past for separating unwanted debris from granular material. Such apparatus has generally required large motors with sufficient horsepower to produce the necessary dynamic forces to separate efficiently the heavier undesired materials from the lightweight granular material. In this regard, brute force type drives, such as drives which do not operate at or near the natural frequency of the vibrating system of which the screen forms a part, usually employ rotary vibrating motion in conjunction with a tilted or inclined screen to achieve the necessary directional movement of the material being screened. Such apparatus has been generally noisy, and has required very sturdy or rugged construction materials to prevent frequent failures due to breakage or material fatigue caused by the rotary vibrating motion.
Therefore, it would be highly desirable to have a new and improved method and apparatus for performing the desired separation in a highly efficient and effective manner, without requiring the use of bulky and expensive motors, and without the unwanted expenditure of excessively large amounts of energy.
Another problem associated with the brute force type drives has been their susceptibility to failure, due to the driving rotary motion associated with vibrating the frame of such devices and their associated screens. Moreover, such devices due to their complexity, have been difficult to maintain and have been limited to processing only certain types of granular material without expensive and costly modifications.
Therefore, it would be highly desirable to have a new and improved method and apparatus of separating undesired debris from granular material in a very reliable manner. Such an apparatus should be inexpensive to manufacture and maintain and should be adaptable for use in cleaning a variety of granular materials without expensive and costly modifications.